Someone tells you to start with £1,000 a month on Facebook and see what happens. Someone else says 10% of revenue. Both are guesses. Neither knows what one of your orders leaves you, and that’s the only thing that decides how much you can safely spend.
Your Facebook ads budget is the number of new customers you want each month, times the most you can afford to pay for each one. That most-you-can-pay figure comes from your profit per order, not from a percentage of revenue.
Monthly Meta budget = new customers wanted × target cost per customer
Why “10% of revenue” doesn’t work
The same percentage can make money for a shop with high margins and lose it for a shop with low ones. And “start with £1,000 a month” says nothing about whether those sales will be profitable. Start from what an order leaves you.
Step 1: find your break-even ROAS
Take your order price before VAT. Take off the costs that rise with every sale: the product itself, shipping and packing, payment fees, and returns and refunds. What’s left pays for ads and profit.
Say your order is £80 before VAT:
£80 ÷ £38.40 = 2.1. Every £1 on ads has to bring back £2.10 of sales just to stand still.
Move the sliders to find yours:
Try it with your numbers
Your break-even ROAS
Where each order goes
- Product
- Shipping
- Fees
- Returns
- Left for marketing
Left for marketing: £ an order
Aim for a target ROAS of ×, 20 to 30% above the floor.
Add your fixed costs (monthly view)
Staff, rent and software don't rise with each sale, so they stay out of the floor. To see the MER you need to cover them too in a month, add them here.
To cover fixed costs as well, this month needs an MER of ×.
Step 2: set your target
Aim 20 to 30% above break-even. That leaves room for a bad week.
At a target of about 2.6×, you can pay up to £31 to win a first order of £80.
If customers come back and order again, you can pay more. CAC vs LTV shows how.
No more guessing at a test budget. Get a number you can trust, built on your own costs.
Step 3: work out the budget
That’s your starting point. Real results will move with your creative, your product pages and the time of year. Check it against your actual ROAS after four weeks.
Make sure the test is big enough
Meta’s own guidance is around 50 purchases per ad set in a week before a campaign finishes learning.
That’s roughly £6,700 a month for one ad set.
If that’s more than you want to spend, don’t spread a small budget across lots of ad sets. Run one campaign with one or two ad sets and give it longer. Easier Ads Budgeting works out the spend and the number of weeks a fair test needs, from your price, VAT and per-order costs.
When to spend more, and when to pull back
- Spend more once ROAS has held above your target for three weeks or more. Raise the budget 15 to 20% a week. At 15% a week, a budget roughly triples in eight weeks.
- Pull back when ROAS stays below break-even for several weeks and fresh creative hasn’t helped. Drop to a smaller budget while you fix the cause, rather than switching off.
- Watch retargeting. It always reports a high ROAS, because it reaches people who were already close to buying. Most of your budget should go on reaching new people.
Where fixed costs fit
Staff, rent and software stay the same whether you sell 100 orders or 1,000. Keep them out of break-even ROAS. Once a month, check that your profit after ads covered them.
Free tools to go further
- Easier Ads Budgeting: how much a new Meta test needs to spend, and for how long
- Easier Profit Calculator: coming soon
- Free Black Friday audit: we check your Meta account before the busiest weeks
- Break-even ROAS: the floor from Step 1, in more depth
- How to split your marketing budget: where Meta fits next to Google and email
The busiest weeks are when a winning campaign slips below break-even unnoticed. Let's keep yours safe.
Want a second pair of eyes on your Meta budget? Book a free call and we’ll work it out with you.
Quick answers
How do I work out my Facebook ads budget?
Find the most you can pay for a new customer from your profit per order, then multiply by the number of new customers you want each month. That is your starting budget.
What percentage of revenue should go to Facebook ads?
A percentage of revenue ignores your costs, so the same figure can be profitable for one shop and loss-making for another. Work from your profit per order and break-even ROAS instead.
What is the minimum budget for a Facebook ads test?
Meta's own guidance is around 50 purchases per ad set in a week to finish learning. If that is more than you can spend, run fewer ad sets and give the test longer. Easier Ads Budgeting works out the budget and time for you.
How fast should I increase my Facebook ads budget?
Once ROAS has stayed above your target for at least three weeks, raise the budget by 15 to 20% a week. Bigger jumps can send campaigns back into learning.
Do staff and software costs go into the calculation?
No. Break-even ROAS uses only costs that rise with every sale. Check fixed costs separately, once a month.
